Method for improving removal rate of arsenic in tire cord steel produced by converter

Abstract

The invention belongs to the technical field of pure steel smelting, and particularly relates to a method for improving the removal rate of arsenic in tire cord steel produced by a converter. Comprising the following steps: S1, controlling arsenic in molten iron entering a furnace to be less than or equal to S2, a double-flow-channel oxygen lance is adopted for top-blowing oxygen supply and a high-low-high mode; s3, mixed gas of N2 and Ar is subjected to bottom blowing stirring, carbon powder is added into the molten pool in the later period of blowing, and a weak reducing atmosphere is created at the temperature larger than or equal to 1250 DEG C; s4, the final slag alkalinity CaO / SiO2 of the converter is controlled to be 2.8-3.2, and the FeO content is 12%-16%; and S5, the flue gas temperature is controlled to be 374 + / -5 DEG C, the residual oxygen content is controlled to be 4.3%-5.0%, As2O3 is oxidized into As2O5, and arsenic trapping is achieved through a wet electrostatic dust collector or alkali washing. According to the method, the arsenic removal rate is increased from less than 10% to more than or equal to 50%, and the As content of the tire cord steel is less than or equal to 0.006%.

Description

Technical Field

[0001] This invention belongs to the field of clean steel smelting technology, specifically relating to a method for improving the arsenic removal rate in converter-produced cord steel. Background Technology

[0002] Cord steel is a key raw material for manufacturing steel cord, the reinforcing skeleton material for radial automotive tires. It places extremely stringent requirements on the cleanliness, uniformity, and strength of the steel. In particular, residual arsenic (As) severely degrades the steel's drawability and fatigue life; therefore, advanced standards require its content to be ≤0.006%. However, in the oxidizing atmosphere of converter steelmaking, arsenic's affinity for oxygen is much weaker than that for iron, resulting in extremely low arsenic removal rates (typically <10%) in conventional smelting, making its removal a global challenge. Existing technologies attempt to promote arsenic volatilization by increasing temperature, but this easily leads to increased furnace lining corrosion and iron loss; and improperly treated arsenic volatilized into flue gas can cause serious secondary environmental pollution. Therefore, developing a green and efficient method that can synergistically solve the two major challenges of "deep arsenic removal from molten steel" and "arsenic pollution in flue gas" is an urgent technological breakthrough needed in this field. Summary of the Invention

[0003] To achieve the above objectives, this invention provides a method for improving the arsenic removal rate in converter steel production. The core innovative idea is to regard arsenic removal as a "migration" process that runs through the entire steelmaking process. By creating optimal thermodynamic and kinetic conditions at each stage, the method guides the arsenic to transfer in a directional and efficient manner from "molten iron → molten steel → slag / gas phase → flue gas → recovered products", and ultimately achieves resource recovery.

[0004] The technical solution of this invention is a method for improving the arsenic removal rate in converter steel production, comprising the following steps:

[0005] S1: During the hot metal pre-control stage, the arsenic content of the hot metal entering the furnace is controlled to be ≤0.015%, and the sulfur content of the hot metal after KR desulfurization pretreatment is ≤0.002%.

[0006] S2: In the converter intensified blowing stage, a dual-channel oxygen lance is used for top blowing oxygen supply, with the main nozzle oxygen supply intensity at 4.0–4.2 m. 3 / (t·min), during the middle stage of blowing, the auxiliary nozzle gas is switched to CO2, and the oxygen lance position executes the high-low-high mode;

[0007] S3: Molten pool stirring and reducing atmosphere creation stage, using a N2 and Ar mixed gas with a volume ratio of 7:3 for bottom blowing stirring throughout, with an intensity of 0.025~0.040m. 3 / (min·t); Carbon powder is added to the molten pool in the later stage of blowing to create a weak reducing atmosphere, and the temperature of the molten pool is controlled to be ≥1250℃ during this stage;

[0008] S4: The stage of precise control of slag composition, controlling the basicity of converter final slag CaO / SiO2 between 2.8 and 3.2, and the FeO content between 12% and 16%; lime is added in batches, with the first batch of lime accounting for 1 / 3 of the total amount;

[0009] S5: The stage of directional conversion and capture of arsenic in flue gas. The converter flue gas is introduced into the waste heat boiler, and the flue gas temperature is controlled at 374±5℃ and the residual oxygen content is within the range of 4.3% to 5.0%, so that gaseous As2O3 is oxidized to As2O5. Then the flue gas is purified and captured by a wet electrostatic precipitator or an alkaline scrubbing tower.

[0010] Furthermore, the converter intensified blowing stage follows a high-low-high pattern, with the lance position at 2.0m in the early stage, 1.2m in the middle stage, and 1.8m in the final stage.

[0011] Furthermore, in the stage of stirring the molten pool and creating a reducing atmosphere, the amount of carbon powder added is 0.5 to 1.0 kg / ton of steel.

[0012] Furthermore, it also includes recovering high-purity elemental arsenic from the arsenic-containing dust captured in S5 as a secondary resource through hydrometallurgical processes.

[0013] The key technological innovation of this invention lies in:

[0014] 1. A synergistic oxidation-reduction mechanism for arsenic volatilization: This innovative approach combines high-intensity oxidation (rapid heating and mass transfer) with a weak reducing atmosphere in the later stages of smelting (achieved through bottom blowing of N2 / Ar and carbon injection). Early oxidation provides a high-temperature foundation for later reduction, while the later oxidation process alters the form of arsenic, promoting the formation of As4(g), thus significantly enhancing the driving force and rate of arsenic volatilization.

[0015] 2. Control of Arsenic Migration Pathways in the Slag-Gas Competition: By precisely controlling the slag basicity (R = 2.8–3.2) and FeO content, the slag is transformed from an "arsenic trap" into an "arsenic transport medium." This avoids the formation of stable Ca3(AsO4)2 under high basicity, ensuring the smooth release of arsenic from the slag into the gas phase and opening up the critical migration pathway of arsenic from molten steel to flue gas.

[0016] 3. Integrated flue gas treatment strategy of "conversion-capture": By setting a specific temperature (374±5℃) and residual oxygen window in the flue gas system, the main volatile arsenic compound As2O3 is directionally oxidized into As2O5, which is easier to capture by wet scrubbing. Subsequently, combined with WESP and alkaline washing, the efficient solidification and recovery of arsenic is achieved, transforming end-of-pipe treatment into resource recovery.

[0017] The beneficial effects of this invention are:

[0018] (1) This invention achieves a technological breakthrough and a leapfrog improvement in arsenic removal efficiency by using full-process collaborative control to steadily increase the arsenic removal rate of converters from the industry average of <10% to ≥50%.

[0019] (2) By adopting the technical solution of the present invention, ultra-clean cord steel with an As content ≤0.006% can be stably produced, and the cleanliness of the product reaches the top level, meeting the stringent requirements of high-end products for residual elements in materials.

[0020] (3) This invention innovatively oxidizes and efficiently captures gaseous arsenic in flue gas with a capture rate of >95%, and can recover high-purity elemental arsenic through subsequent processes, realizing the resource utilization of hazardous waste and completely solving the problem of secondary arsenic pollution.

[0021] (4) The present invention optimizes parameters and re-engineers processes based on existing converter smelting equipment, requires no major fixed asset investment, has controllable production costs, and is easy to promote and implement in steel enterprises. Detailed Implementation

[0022] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention.

[0023] Example 1:

[0024] This embodiment involves the production of 72A grade cord steel using a 100t converter, and the steps are as follows:

[0025] (1) Pre-control of molten iron: The proportion of high-arsenic ore was reduced from 20% to 8%, and the As content in molten iron was reduced from 0.015% to 0.008%;

[0026] (2) Enhanced oxygen supply: The oxygen supply intensity of the dual-channel oxygen lance is 4.1 m. 3 / (t·min), mid-term secondary nozzle switching to CO2;

[0027] (3) Bottom-blown reduction: N2 / Ar mixture intensity 0.030m 3 / (min·t), add 0.8kg / t of carbon powder 8 minutes before the endpoint; preferably add it 8 to 10 minutes before the endpoint to ensure sufficient time to create a reducing atmosphere and promote arsenic volatilization, while avoiding excessive interference with the endpoint carbon control.

[0028] (4) Slag control: final slag R=3.0, FeO=14%, and the residual rate of As slag is reduced to 35%;

[0029] (5) Flue gas treatment: The outlet temperature of the waste heat boiler is controlled at 374℃ and the residual oxygen is 4.3% to oxidize As2O3 to As2O5; the electrostatic precipitator temperature is 287℃ and the arsenic solidification rate of flue gas is 96.2%. Around 374℃ is the ideal temperature range for the oxidation kinetics of As2O3. Too high a temperature may cause As2O5 to decompose again, while too low a temperature will result in a slow oxidation reaction rate.

[0030] Performance test: As in molten steel = 0.006%, removal rate 61%.

[0031] Example 2:

[0032] This embodiment involves the utilization of arsenic resources from flue gas in a 100t converter, and the steps are as follows:

[0033] (1) Pre-control of molten iron: The proportion of high-arsenic ore was reduced from 19% to 5%, and the As content in molten iron was reduced from 0.0146% to 0.008%;

[0034] (2) Enhanced oxygen supply: The oxygen supply intensity of the dual-channel oxygen lance is 4.0 m. 3 / (t·min), mid-term secondary nozzle switching to CO2;

[0035] (3) Bottom-blown reduction: N2 / Ar mixture intensity 0.030m 3 / (min·t), add 0.8kg / t of carbon powder 8 minutes before the endpoint; preferably add it 8 to 10 minutes before the endpoint to ensure sufficient time to create a reducing atmosphere and promote arsenic volatilization, while avoiding excessive interference with the endpoint carbon control.

[0036] (4) Slag control: final slag R=3.0, FeO=14%, and the residual rate of As slag is reduced to 35%;

[0037] (5) Flue gas treatment: The As2O3 recovered by condensation is purified by wet process, dissolved in 70% sulfuric acid, and reduced by SnCl2 / HCl to obtain 99.9% elemental arsenic.

[0038] Performance test: As in molten steel = 0.005%, removal rate 60%.

[0039] Table 1 compares the typical effects of the method of the present invention with those of conventional methods.

[0040]

[0041] As shown in Table 1, the technical solution of this invention employs a full-process arsenic removal system of "source pre-control - process enhancement - end-of-pipe recovery". At the source, the arsenic content of the molten iron entering the furnace is controlled to be ≤0.015%. During the process, a dual-channel oxygen lance with main oxygen + CO2 is used, with high-intensity oxygen supply and a "high-low-high" lance position mode. Combined with bottom blowing of N2 / Ar mixed gas and subsequent carbon injection, a weak reducing atmosphere is created at ≥1250℃, which promotes the efficient volatilization of arsenic in the form of As4(g). Simultaneously, the final slag basicity R = 2.8~3.2 and the FeO content is 12%~16% to prevent arsenic from being fixed in the slag. At the end, the flue gas is directionally oxidized at 374±5℃ and residual oxygen 4.3%~5.0% to convert As2O3 into As2O5. Then, wet electrostatic dust removal and alkaline washing are used to achieve efficient arsenic capture and resource recovery of >95%. This invention increases the arsenic removal rate from <10% to ≥50%, stably achieving As ≤0.006% in tire cord steel, and eradicates secondary arsenic pollution.

[0042] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present technical solution are within the protection scope of the present invention.

[0043] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some descriptions of this invention have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements may also constitute the content of this invention.

Claims

1. A method for improving the arsenic removal rate in converter steel production, characterized in that, Includes the following steps: S1: During the hot metal pre-control stage, the arsenic content of the hot metal entering the furnace is controlled to be ≤0.015%, and the sulfur content of the hot metal after KR desulfurization pretreatment is ≤0.002%. S2: In the converter intensified blowing stage, a dual-channel oxygen lance is used for top blowing oxygen supply, with the main nozzle oxygen supply intensity at 4.0–4.2 m. 3 / (t·min), during the middle stage of blowing, the auxiliary nozzle gas is switched to CO2, and the oxygen lance position executes the high-low-high mode; S3: Molten pool stirring and reducing atmosphere creation stage, using a N2 and Ar mixed gas with a volume ratio of 7:3 for bottom blowing stirring throughout, with an intensity of 0.025~0.040m. 3 / (min·t); Carbon powder is added to the molten pool in the later stage of blowing to create a weak reducing atmosphere, and the temperature of the molten pool is controlled to be ≥1250℃ during this stage; S4: The stage of precise control of slag composition, controlling the basicity of converter final slag CaO / SiO2 between 2.8 and 3.2, and the FeO content between 12% and 16%; lime is added in batches, with the first batch of lime accounting for 1 / 3 of the total amount; S5: The stage of directional conversion and capture of arsenic in flue gas. The converter flue gas is introduced into the waste heat boiler, and the flue gas temperature is controlled at 374±5℃ and the residual oxygen content is in the range of 4.3% to 5.0%, so that gaseous As2O3 is oxidized to As2O5. Then the flue gas is purified and captured by a wet electrostatic precipitator or an alkaline scrubbing tower.

2. The method for improving the arsenic removal rate in converter steel production as described in claim 1, characterized in that, The converter intensified blowing stage is in a high-low-high mode, i.e., the lance position is 2.0m in the early stage, 1.2m in the middle stage, and 1.8m in the final stage.

3. The method for improving the arsenic removal rate in converter-produced cord steel as described in claim 2, characterized in that, During the stage of stirring the molten pool and creating a reducing atmosphere, the amount of carbon powder added is 0.5 to 1.0 kg / ton of steel.

4. The method for improving the arsenic removal rate in converter-produced cord steel as described in claim 3, characterized in that, It also includes recovering high-purity elemental arsenic from the arsenic-containing dust captured in S5 as a secondary resource through hydrometallurgical processes.

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